The invention relates to a pinch valve, comprising                an axially extending tube guide,        a clamping jaw which displaces perpendicularly to the axial direction, and        an abutment which is arranged opposing the clamping jaw in the displacement direction of the clamping jaw,wherein the tube guide, the clamping jaw and the abutment are arranged in relation to one another such that a flexible tube laid in the tube guide is pinched against the abutment by the advance of the clamping jaw.        
Pinch valves are known in many variants. For example, from DE 199 17622 C2, there is known a basic type of pinch valve. Pinch valves of this type have a tube guide into which a medium-transporting flexible tube can be laid. The tube guide serves for more or less precise positioning of the tube relative to the pinch valve and a more or less permanent fixing of both elements to one another. The orientation of the tube guide, that is, the orientation of the tube in the mounted state is herein identified as axial or the axial direction. central element of many pinch valves is a clamping jaw which is displaceable perpendicularly to the axial direction toward an abutment. The clamping jaw and the abutment are arranged on either side of the tube guide, that is, the tube guide lies between the clamping jaw and the abutment. In this way, an advance of the clamping jaw, that is, the movement thereof toward the abutment, leads to a narrowing of the free lumen of the tube guide and therefore to pinching of a flexible tube laid in the tube guide. The free lumen of the tube is thereby narrowed to the point of complete closure, so that a medium flow in the tube is reduced or entirely prevented. The force necessary for advancing the clamping jaw can be generated manually or automatically, for example, electromotively or electromagnetically.
From both WO 03/070313 A1 and U.S. Pat. No. 4,518,14 A, valves are known which use tube-shaped elastic sealing elements and operate similarly to the valve described above.
In all of the examples, in order to open the valve again, the advancing force is switched off and, in some cases, the clamping jaw is pulled back. However, if the shape restoring force of the tube is sufficient, the latter is often not necessary. In any event, the shape restoring force of the tube must be at least so great that, supported by the pressure of the medium in the tube, the force is sufficient to restore the original tube form with an open lumen. This requires relatively thick, elastic tube walls and/or a relatively high medium pressure in the interior of the tube. However, this cannot be guaranteed in all cases of use. Particularly in cases of very low medium flow as occurs, for example, in the pharmaceutical and biotechnical industries when handling small quantities of high-value fluids, a very low medium pressure prevails and the tube walls are often extremely thin so that, particularly following long pinching times, the danger exists that the tube opens incompletely or not at all. This must be considered disadvantageous because, particularly in precision processes, a very exactly reproducible medium flow through all conducting elements is required. DE 299 13 774 U1 addresses this problem and proposes, as a solution, guiding a medium-conducting product tube symmetrically surrounded by four pressure medium-filled working tubes in a rigid pipe. The application of pressure to two mutually opposing working tubes leads to pinching of the product tube which lies therebetween and which is able to expand perpendicularly to the pinch direction, since the working tubes are not pressurized at this time point and are therefore pliable. In order to re-open the product tube, the previously pressurized working tubes are de-pressurized and the previously de-pressurized working tubes are pressurized. The product tube is thereby returned to its original form. A disadvantage of this device is the complex design which, for the pinch valve, requires at least two independent pressure medium conduits and pressure generation apparatus which must be regarded as unfavorable in terms of costs, spatial demands and susceptibility.